The invention is based on a fuel injection pump as defined hereinafter.
In Diesel engines, the actual fuel consumption per stroke is known to vary with the rpm. While the supply quantity per stroke of the injection pump increases with increasing rpm, the characteristic curve for the quantity required by the engine drops beyond a predetermined rpm. Therefore the injection quantity at full load must be adapted to what is needed. Injecting too much fuel means that smoke will develop or that the Diesel engine will overheat. Aside from this, the fuel consumption is reduced and the torque characteristic is improved by means of this adaptation.
In known fuel injection pumps of this type (Bosch distributor injection pump, type VE) this full-load adaptation is therefore usually effected by means of the pressure valve on the high-pressure side of the pump and/or by means of an expanded governor lever assembly. A full-load regulation using the governor lever assembly is performed whenever the pressure valves are no longer sufficient for the adaptation, or whenever special, additional characteristics are to be taken into consideration in the adjustment, such as the charge pressure of a turbocharger or the atmospheric pressure.
In addition to the full-load quantity, the supply onset must also be corrected in accordance with load. The load-dependent supply onset is designed such that with decreasing load, for instance decreasing from full load to partial load (retraction of the gas pedal), a shift toward "late" is made. With increasing load, a decrease in the rpm occurs, and the load-dependent supply onset shifts the instant of injection toward "late". Smoother engine operation as well as noise abatement is hereby attained. In a known fuel injection pump of the type mentioned at the outset above i.e., (German Offenlegungsschrift No. 21 58 689), the rpm governor operates with a governor sleeve, which is engaged by the flyweights and which controls a valve by means of which the progression of the supply pump pressure, which increases with increasing rpm, is decreased beyond a predetermined rpm, thereby effecting a shift of the injection adjusting piston and hence of the onset of injection toward "late". Since a specific set-point rpm or a specific load status for which the governor adjusts the required injection quantity, for instance by shifting the governor sleeve, is predetermined by the adjusting lever, this valve effects a load-dependent variation of the supply pump pressure and thus of the injection onset.
In another known fuel injection pump (German Offenlegungsschrift No. 19 12 919), a full-load stop is attained by means of a piston acted upon by the supply pump pressure varying in accordance with rpm, on the jacket face of which is a curve which is picked up by a bell crank, one arm of which serves as the full-load stop of the governor lever of the rpm governor. Any fluctuations in the supply pump pressure simultaneously cause a variation or fluctuation in the adjustment, which in turn causes poorer engine operation.
According to a further development (German Offenlegungsschrift No. 31 21 107) of this known fuel injection pump, a throttle is provided in the inflow conduit to the work chamber of the piston, and a magnetic valve is provided in an outflow conduit of this work chamber; the magnetic valve is triggered in accordance with engine load and rpm by means of an electronic control unit. The required transducer values are picked up from governor elements that are adjustable in accordance with load.
Direct injection engines react to load changes from full to partial load particularly sensitively in terms of a belated correction of the injection onset toward "late". If the injection adjustment lags behind the load change, as in all known fuel injection pumps, this causes worsening consumption, noise and emissions. In vehicle engines, such changes from full load to partial loads are made continually, whenever the gas pedal is retracted.